Microsensor to measure or regulate the amount of chlorine and bromine in water

ABSTRACT

A thick film electrochemical microsensor device for measuring or regulating chlorine and bromine in water, comprising a substrate to which is applied an optimum arrangement of at least two electrodes. The device is especially useful for measuring or regulating chlorine and bromine levels in swimming pool or spa water. A method of measuring or regulating ions of at least one of chlorine and bromine in water is also described, which comprises contacting the water with the microsensor of the present invention; measuring the current output of the microsensor; determining the level of at least one of chlorine and bromine indicated by the current output; and generating a signal.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a division of U.S. Ser. No. 09/799,969 filedon Mar. 6, 2001, which claims priority from U.S. Provisional Application60/187,528, filed on Mar. 7, 2000.

TECHNICAL FIELD

[0002] The present invention is directed to a microsensor device formeasuring or regulating at least one of chlorine and bromine ions. Moreparticularly, the invention is directed to a thick film electrochemicalmicrosensor capable of measuring or regulating the level of chlorine andbromine ions in swimming pool or spa water. The invention furtherencompasses a method of measuring or regulating the levels of chlorineand bromine ions in swimming pool or spa water using the electrochemicalmicrosensor.

BACKGROUND OF THE INVENTION

[0003] In order to insure that the water in a pool or spa is safe, itmust be properly sanitized to prevent any health problems arising due toalgae, bacteria, or any other pathogens which may be in the water.Currently, chlorine and bromine are commonly used to sanitize pools orspas. The chlorine comes in a number of different forms: sodiumhypochlorite (liquid bleach), calcium hypochlorite, lithium hypochloriteor chlorinated isocyanurates. When any of these materials interact withwater, they undergo hydrolysis to form free chlorine consisting ofpredominantly hypochlorous acid (HOCl), which is the sanitizing agent,and hypochlorite ion. Free available chlorine (FAC) is the amount ofunused or unreacted chlorine. Combined available chlorine (CAC), alsoknown as chloramines, is the portion of chlorine which has interactedand combined with contaminants. For the purposes of this invention,measurement of chlorine refers to the chlorine ion Cl⁻¹, as well ashypochlorous acid HOCl, and hypochlorite ion OCl⁻¹.

[0004] The National Spa and Pool Institute recommends 1 to 3 parts permillion of free chlorine in the water and a pH between 8 and 10. Mostpool or spa owners use a visual test which measures the amount of totalchlorine in the water, not the amount of free available chlorine. Thisvisual test can be incorrectly performed or inaccurately interpreted,and the wrong amount of chlorine may then be added to the water. Thisinaccuracy often leads to an unwanted chlorine odor, red, burning eyes,or the spread of diseases among the swimmers.

[0005] Electrochemical sensors have been used in various fields becauseof their cost effective mode of operation and uncomplicated method ofmanufacture. U.S. Pat. No. 5,676,820 to Wang et al. describes a sensorused to monitor metal contaminants in a remote location, connected via acommunications cable to an analysis device. Microsensors have also beenused to detect acidity in water, as well as to monitor species such ascarbon dioxide and hydrogen sulfide.

[0006] It is therefore an object of the present invention to provide athick film electrochemical microsensor for measuring or regulating atleast one of chlorine and bromine in water such as swimming pool and spawater.

SUMMARY OF THE INVENTION

[0007] The present invention provides an electrochemical microsensordevice for measuring or regulating ions of at least one of chlorine andbromine comprising, a substrate supporting an arrangement of at leasttwo electrodes, wherein one of the electrodes is an anode and one of theelectrodes is a cathode, wherein the electrodes are formed or fabricatedusing a thick film technique, and wherein the anode is adapted foroxidation of chlorine and bromine ions.

[0008] The present invention further provides a method of measuring orregulating ions of at least one of chlorine and bromine in watercomprising contacting the water with the electrochemical microsensordevice of the invention, measuring the current output of the sensor,determining the level of chlorine and bromine indicated by the currentoutput, and generating a signal.

[0009] It has been found that chlorine and bromine can be measured inwater using a thick film electrochemical microsensor device. Novelelectrode configurations were designed and tested, and the results arereported herein, along with a preferred electrode configuration.

[0010] Advantageously, the thick film electrochemical microsensor deviceof the present invention can be used to actuate a regulating means tomaintain an appropriate level of chlorine and/or bromine in swimmingpool or spa water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic illustration of the design of 8 thick filmelectrochemical microsensors prepared and tested in accordance with theinvention.

[0012]FIG. 2 is a graphical representation of the current output for thesensor of example no. 1 in relation to chlorine ion concentrations from0.0 to 2.0%.

[0013]FIG. 3 is a graphical representation of the current output for thesensor of example no. 4 over a range of voltages from 0 to 1.2 V.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention is directed to a thick film electrochemicalsensor device that is capable of being used to measure or regulatechlorine and bromine ion levels in water such as swimming pool or spawater.

[0015] More specifically, the present invention is directed to thefabrication and use of a chip-like thick film electrochemicalmicrosensor device with at least two electrodes, including an anode anda cathode, arranged on an inert substrate. The overall size of themicrosensor device can vary greatly, dependent only on economicefficiency and user preference.

[0016] The microsensor device of the present invention is anelectrochemical system in which a reversible redox reaction takes place.Electrochemical methods of analysis include all methods of analysis thatmeasure current, potential and resistance, and relate them to analyteconcentration. Voltammetric techniques have been classified as dynamicelectrochemical techniques. In their operation the potential iscontrolled and the current is monitored. Voltammetric techniques arebased on the measurement of current as a function of potential. Thecurrent is produced at an electrode surface following the oxidation orreduction of the analyte at a characteristic potential. Oxidation orreduction at the electrode surface is essentially electron-transfer (orcharge transfer). In any voltammetric technique it is the chargetransfer that is being measured. The current is measured in amperes i.e.the rate of flow of charge. Voltammetric measurements are thereforemeasurements of the rate of reaction. The electrochemical reaction atthe electrode surface is driven by the application of a potential tothat electrode. The applied potential is the excitation signal and themeasured current is the resulting signal. The potential at which thereaction occurs is characteristic of the analyte, based on the Gibbsfree energy for the reaction, and the amount of current that is measuredis related to concentration.

[0017] The sensor is preferably made using a thick film technique,including deposition of multiple electrodes on a substrate.Electrochemical sensors and thick film techniques for their fabricationare discussed in U.S. Pat. No. 4,571,292 to C. C. Liu et al, U.S. Pat.No. 4,655,880 to C. C. Liu, and co-pending application U.S. Ser. No.09/466,865 to Lai et al, which patents and application are incorporatedby reference as if fully written out below.

[0018] The substrate may be formed of plastic, glass, ceramic, alumina,quartz, or any other material that preferably is inert relative to thematerial from which the electrodes are formed and the material intowhich the sensor is intended to be placed for use. Preferably thesubstrate is an alumina ceramic material. Other suitable ceramicsinclude aluminum nitride, silicon carbide, silicon nitride, and thelike.

[0019] The multiple electrodes include at least one each of an anode anda cathode. The anode is the working electrode, and should preferably becomposed of a material that is inert relative to the substrate and thechlorine and bromine. The working electrode functions, via oxidation ofchlorine and bromine ions, to draw current flow detectable by knownmeasuring means. Examples of materials suitable for the anode include,but are not limited to, gold, platinum, palladium, silver, and carbon.Preferred materials are platinum or gold. Platinum, for example, isapplied to the substrate in the form of a platinum ink, which iscommercially available, or can be made using finely dispersed metalparticles, solvent, and a binder. Ultra violet (UV)-cured platinum inkis commercially available, and can also be used in forming theelectrodes.

[0020] Specific examples of suitable materials to form the cathode aresilver-silver chloride and mercury-mercuric chloride (Calomel).Silver-silver chloride is preferred. The silver is applied to thesubstrate in the form of a silver ink, which is commercially available,or can be made using finely dispersed metal particles, solvent, and abinder. Ultra violet (UV)-cured silver ink is commercially available,and can also be used in forming the electrode. As described in furtherdetail herein, the silver is exposed to chloride solution to produce thesilver-silver chloride electrode.

[0021] The electrodes of the sensor apparatus of the present inventionmay include a connect portion and a sensing portion. The sensing portionof the electrode is exposed to the environment, and is in contact withthe electrolyte and the target species. The sensing portion functions todetect the target species as discussed above. The connect portion of theelectrode connects the electrode to an electrical circuit, and isprotected from the environment by an insulator. The insulator used toprotect the connect portion of the electrodes of the present inventionis preferably glass, and is applied in the form of an insulating ink. Ina preferred embodiment, wires are soldered to the connect portion of theelectrodes using indium solder. The wires and the solder are thencovered with a silicone paste.

[0022] The arrangement of the electrodes on the substrate is important.The cathode (reference electrode) is placed close to the anode (workingelectrode). The shapes of the electrodes are important, as is their sizeor any modification to their surfaces.

[0023] According to the invention, sensor designs were drawn onAUTO-CAD™, a computer drafting program. Then, through a thick filmprocess, which is similar to the silk screening process, silver,platinum, and insulating precursor inks were printed onto aluminaceramic substrates to form the electrodes. The silver was treated withchloride to form silver-silver chloride, the material used for thecathode, and platinum was used for the anode. The microsensors wereheated to solidify the components, the wires were soldered to thecontacts, and silicone paste was applied and cured. Finally, the sensorswere tested by exposure to chlorine and bromine concentrations of fromabout 0 to about 2.0%.

[0024] To use the microsensor device, a voltage must be applied and thecurrent measured. The voltage used depends on the target species and thetype of electrodes. The corresponding current produced is measured andused to quantify the concentration of the target species, namelychlorine and bromine ions.

SPECIFIC EMBODIMENTS OF THE INVENTION

[0025] The sensor configurations fabricated and tested according to theinvention are shown in FIG. 1. Sensor examples nos. 1-8 are numberedaccordingly. Sensor example no. 1 comprises an anode 9, a cathode 10,and contacts 11, 12, where connecting wires are attached, arranged on asubstrate 13. As shown in FIG. 1, each sensor configuration comprises ananode 9, and a cathode 10, with differences in shape, size, andplacement on the substrate.

[0026] Results of tests done on sensor example no. 1 are shown in FIG.2. The current output is plotted versus the concentration of chlorine inthe test solutions, which ranges from 0 to 2.0 percent. The data shownin FIG. 2 was measured at 0.5 V.

[0027] Results of tests done on sensor example no. 4 are shown in FIG.3. The current output is plotted versus the applied potential, which wasvaried over a range of 0 to 1.0 V. Line nos. 14 to 17 correspond to testsolutions of 0.5, 1.0, 1.5, and 2.0% chlorine ions, respectively.

EXPERIMENTAL PROCEDURES

[0028] The thick film microsensors according to the invention werefabricated according to the procedure below.

[0029] Eight designs were developed and drawn using an AUTO-CAD™program. They were then converted into screen patterns by one of thefollowing methods. 1.) The designs were magnified ten times and readinto a program called SHADI, which directed the RUBYLITH™ cutter to cutthe designs onto a plastic RUBYLITH™ material. The outer coating of theRUBYLITH™ was peeled away from the interior of the design, leaving thedesign clear. This design was then placed over a light source and aphotographic plate was exposed leaving the design black when developed.2.) The interior of the eight designs were filled in black using theAUTO-CAD™ program. The designs were printed out onto transparencies,which were then cut into four by four inch squares.

[0030] The resulting pattern was placed onto a sheet of photosensitiveplastic. The plastic was placed under ultraviolet light, exposing theplastic where there was no design. The unexposed portions were removed,and the plastic was attached to a metal screen. The metal screen wasplaced into a metal frame to form a template. A separate template wasprepared for each electrode and for the insulator ink.

[0031] The templates were then used with a thick film printer to “silkscreen” the patterns onto a ceramic substrate. A template was contactedwith the substrate, and placed into the printer. The printer firstapplied the platinum precursor ink onto the substrate, according to thepattern of the template. Next, the silver was applied. Finally, theinsulator ink was applied. Transferring the pattern from the template tothe substrate in this manner forms a sensor configuration on thesubstrate.

[0032] After the precursor inks had been applied, the substrate wasplaced in a drying oven at about 100° C., and then fired in a furnace atabout 850° C. to cure the electrode precursors and solidify the sensordevice.

[0033] Afterwards, the substrates were diced using a diamond saw intoindividual devices. The resulting sensor devices were approximately 0.75inches wide by 0.75 inches long. The wires were soldered to the connectportion of the sensor device using a soldering iron, flux, and indiumsolder. The connect portion of the sensor device was then covered withinsulation, such as silicone. The silver electrode of the sensor devicewas cleaned using a mechanical pencil eraser. 0.1M hydrochloric acidsolution was placed in a beaker. A platinum screen was connected to thenegative (cathodic) side of a potentiostat. The wire attached to thesilver electrode was connected to the positive (anodic) side of thepotentiostat. Both the platinum screen and the sensor device were placedinto the beaker of 0.1M hydrochloric acid without allowing them to touchone another. A voltage of 0.5 V was applied. The silver surface wasfirst cleaned by turning the power up for 5 seconds and down for 5seconds three times. Then the chloride was allowed to react with thesilver to form silver-silver-chloride by leaving the power on for 2minutes. The sensor was rinsed using warm water and de-ionized water,and placed on paper towels to dry.

[0034] Testing was done using solutions containing concentrations ofchlorine in the amount of 0.5, 1.0, 1.5, and 2.0 percent. The sensor tobe tested was connected to a potentiostat. The silver-silver chlorideelectrode was connected to the negative (cathodic) side of thepotentiostat, and the platinum (working) electrode was connected to thepositive (anodic) side of the potentiostat. A voltage was applied frombetween 0 to about 1.1 V. The current required to effect the oxidationof chlorine ions to chlorine atoms was measured for each solution.Calculations were made relating current output to concentration ofchlorine in the solution, and to voltage. Typical results are shown inFIGS. 2 and 3, respectively. A summary of regression factors R for eachof the sensor examples 1-8 for the plot of current versus chlorineconcentration at 0.5 V is shown in Table 1. As can be seen from the datain Table 1, microsensor example no. 1 appears to show the bestcorrelation between chlorine concentration and current output. This wasalso evident at other voltages tested. TABLE 1 R Values at 0.5 V forPlot of Current versus Chlorine Concentration Sensor Example No. R Value1 0.994270 2 0.817087 3 0.766172 4 0.495908* 5 0.849220 6 0.517890 70.783139 8 0.703463

[0035] Further testing was done, as described above, usingconcentrations of bromine in the amount of 0.5, 1.0, 1.5 and 2.0percent. In addition, mixed solutions containing both chlorine andbromine were tested. Results are summarized in Table 2. As can be seenfrom the data in Table 2, microsensor examples 1 and 5 gave the bestresults. TABLE 2 Sensor No. 1 2 3 4 5 6 7 8 Solution Br Br Br Br Br BrBr Br Best R²-Value .9627 .8959 .9524 .9346 1 .5768 .2076 .7798 Voltage1.0 1.0 1.0 1.0 .5 1.0 .9 .8 Solution X % Cl X % Cl X % Cl X % Cl X % ClX % Cl X % Cl X % Cl and and and and and and and and 1% Br 1% Br 1% Br1% Br 1% Br 1% Br 1% Br 1% Br Best R-Value .9206 .8389 .9602 .8890 .9581.4382 .9936 .7065 Voltage 1.1 0.4 0.1 1.1 1.0 0.7 0.7 1.0 Solution 1% Cl1% Cl 1% Cl 1% Cl 1% Cl 1% Cl 1% Cl 1% Cl and X % and X % and X % and X% and and and and Br Br Br Br X % Br X % Br X % Br X % Br Best R-Value.9824 .9686 .9925 .9589 — .9996 .9681 .6538 Voltage 1.1 0.15 0.2 0.15 —1.1 0.1 0.9

[0036] Solutions containing lower levels of chlorine and bromine werealso tested using microsensors 1 and 5. Test solutions were prepared tocontain 25, 50, 75 and 100 parts per million chlorine or bromine.Results are summarized in Table 3. TABLE 3 Sensor No. 5 1 5 Solution ClBr Br Best R-Value .9962 .9546 .9871 Voltage .7 .7 .7

[0037] Sensor example no. 1 provided the best correlation betweencurrent output and chlorine concentration. Sensitivity was good even atlow voltages of around 0.3 V. The electrode configuration for sensorexample no. 1 comprises a rounded anode disposed within the cathodewhich has a concentric arm design. Another preferred embodiment, sensorexample no. 5, gave reasonably good results. The electrode configurationfor sensor example no. 5 comprises a cathode that is a square armdisposed within and surrounded on three sides by a similarly shapedanode.

[0038] Advantageously, the microsensor device of the present invention,prepared using a thick film technique, is relatively inexpensive tomanufacture, install, and operate. For this reason, it is possible touse dual sensors and operate them in a differential mode. In a preferredembodiment, two substantially identical sensors are used. One sensor isoptimized for chlorine and bromine detection, and the second sensor isadapted to detect interference from other chemical species, through theuse of an electrode catalyst or other means. The levels of chlorine andbromine can then be determined by subtracting the signal due to theinterference from the signal of the chlorine and bromine detectingsensor. Such a method of differential operation can overcome theproblems of interference that are known in the art of electrochemicalsensors.

[0039] The method of this embodiment comprises contacting the water witha first inventive sensor adapted to detect chlorine and bromine,measuring the current output of the sensor, generating a first signalbased on the current output of the sensor, providing a second inventivesensor, which has been adapted to detect interferences from otherchemical species, contacting the water with the second sensor, measuringthe current output of the second sensor, generating a second signal, andsubtracting the second signal from the first signal. This signal canthen be used to activate a display device, a recording means, an alarmdevice, and/or a regulating means.

[0040] It is demonstrated that the electrochemical microsensor device ofthe present invention can be used to measure chlorine and brominecheaply and quite effectively in various locations, including swimmingpools and spas. When chlorine and bromine levels are determined, thesensor generates a signal that is sent to an indicator, such as analarm, or visual display, or to a recorder, making it possible to studytrends and track chlorine and bromine levels over a period of time.Current flow can be measured by a potentiostat, for example, or analyzedby computer or another electronic measuring device. The sensor cangenerate a visual or audible alarm signal when the concentration ofchlorine ions is determined to be outside a predetermined range.Additionally, the sensor can generate a signal that is amplified ifnecessary, and that triggers an actuator, to activate a regulatingmeans, such as an existing chlorine dispenser, only when predeterminedlevels of chlorine and bromine are measured, or to inactivate thechlorine or bromine dispenser, allowing more efficient utilization ofthe dispensing system.

[0041] It should now be apparent that various embodiments of the presentinvention accomplish the object of this invention. It should beappreciated that the present invention is not limited to the specificembodiments described above, but includes variations, modifications, andequivalent embodiments defined by the following claims.

1. An electrochemical microsensor device for measuring or regulatingions of at least one of chlorine and bromine comprising, a substratesupporting an arrangement of at least two electrodes, wherein one of theelectrodes is an anode and one of the electrodes is a cathode, whereinthe electrodes are formed using a thick film technique, wherein theanode and the cathode are disposed adjacent to each other, and oneelectrode is substantially nested within the other electrode, andwherein the anode is adapted for oxidation of ions of said at least oneof chlorine and bromine.
 2. The electrochemical microsensor device ofclaim 1, wherein the substrate is an insulating material selected fromthe group consisting of plastic, glass, ceramic, quartz, and mixturesthereof.
 3. The electrochemical microsensor device of claim 1, whereinthe substrate is alumina.
 4. The electrochemical microsensor device ofclaim 1, wherein the anode comprises a material selected from the groupconsisting of gold, platinum, palladium, silver, and carbon.
 5. Theelectrochemical microsensor device of claim 1, wherein the cathodecomprises a material selected from the group consisting of silver-silverchloride and mercury-mercuric chloride.
 6. The electrochemicalmicrosensor device of claim 1, wherein said electrodes comprise aconnect portion and a sensing portion, wherein said connect portion ofthe electrodes connects the electrode to an electrical circuit, and isprotected from the environment by an insulator, and wherein said sensingportion of the electrodes is exposed to the environment.
 7. Theelectrochemical microsensor device of claim 1, wherein the thick filmtechnique comprises: providing at least one template containing apattern for the arrangement of the electrodes; contacting the substratewith the template; applying at least one electrode precursor ink, andinsulator precursor ink onto the template/substrate to form a sensorconfiguration according to the template pattern; drying the sensorconfiguration; and firing the sensor configuration.